BAGHDAD—A series of bombings struck Baghdad and towns south of the Iraqi capital on Thursday, killing at least 22 and wounding dozens in areas that are home to mostly Muslim Shiites—the latest evidence of rising sectarian discord in Iraq.

The attackers struck a day before tens of thousands of Sunni Muslims are expected to take to the streets in what have become weekly protests against the Shiite-led government of Prime Minister Nouri al-Maliki. The rallies are exacerbating long-simmering tensions between Iraq's Sunnis and the Shiite majority nearly a decade after the U.S.-led invasion.

The deadliest attack occurred around sunset when a pair of bombs exploded nearly simultaneously in Shula in northwestern Baghdad. One was a car bomb that was detonated outside a fast food restaurant and the other blast occurred near a soccer field. The twin bombings killed 15 people and left at least 40 wounded, officials said.

There was no immediate claim of responsibility, but car bombings in Shiite areas are a favorite tactic of Sunni extremists such as al-Qaida's local affiliate. The group, known as the Islamic State of Iraq, considers Shiites to be heretics and accuses them of being too closely aligned with neighboring Shiite powerhouse Iran.

Earlier in the day, a car bomb tore through the crowded livestock market in the town of Aziziyah, 55 kilometers (35 miles) southeast of Baghdad. That attack killed three people and wounded eight.

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A few hours later, a roadside bomb missed a passing police patrol in western Baghdad but killed a bystander and wounded eight people.

In the evening, explosives hidden beneath produce in the back of a pickup truck exploded in the town of Mahmoudiya, about 30 kilometers (20 miles) south of Baghdad. That blast killed three policemen and wounded six.

Police and hospital officials provided details of the attacks and the casualty figures. They spoke on condition of anonymity because they were not authorized to talk to the media.

Violence in Iraq has fallen since the height of sectarian fighting in 2006 and 2007, but deadly attacks still happen frequently.

The latest attacks appear designed to undermine confidence in the Shiite-led government. For the past two months, Sunni Muslims have been protesting what they describe as unfair treatment by the country's Shiite-led government. The protests have been largely peaceful.

Ammar Qassim, a resident of the Shula neighborhood where the two bombings occurred, blamed the attacks on political squabbling.

"This tragic security breach took place because the politicians and the leaders of this country are busy with their political conflicts. They should be brave enough to bear the responsibility for the victims falling daily in this country," he said.

Meanwhile, Iraqi authorities released a new batch of inmates from a Baghdad prison in a move aiming at calming the Sunni protesters. Deputy Prime Minister Hussain al-Sharistani announced the release of 160 prisoners, including 13 women, during a ceremony at the prison on Thursday.

He said 4,000 prisoners have been released since a government committee was set up earlier this year to consider protesters' demands. The Sunni protests were sparked by the arrest of bodyguards assigned to Finance Minister Rafia al-Issawi, a senior Sunni politician, in December.

Thursday's bombings marked the fourth time this month that insurgent attacks have claimed more than 20 lives in a single day. More than 160 people have been killed in violent attacks in Iraq since the start of February, according to an Associated Press count.